Library: width=3 feet and length=4 feet ([3x2]+[4x2]=6+8=14). This means that the screen in the auditorium has a width of 15 feet (3x5=15) and a length of 20 feet (4x5=20). So the perimeter of the screen= (15x2)+(20x2)=30+40=70. The perimeter of the screen in the auditorium is 70 feet.